1. Field of Invention
This invention relates to the process of forming roadway markers that are used for traffic lane delineation, in particular, to markers used as lane divider with enhanced reflectivity and abrasion resistant.
2. Related Art
Roadway markers are adhered to pavements along centerlines, edge lines, lane dividers or guardrail delineators. Other roadway markers are used as temporary lane dividers in temporary constructions, detours or prior to permanent marking of newly paved roadways. Since 1965, the most commonly used retroreflective roadway markers are based on Heenan U.S. Pat. No. 3,332,327, Balint U.S. Pat. No. 3,409,344, or Edouart U.S. Pat. No. 4,991,994. Typically, this type of markers are produced in a process consisting of three to five steps: Firstly, injection molding of a thermoplastic shell, either integrally molded with the reflective face, or the reflective faces welded on a corresponding open recesses within the shell. The reflective face, having about 350 or more cube corner reflective elements on each reflective face of the shell. Secondly, either the reflective faces within a shell or the entire inside surface of the shell coated with a reflective metallic sealer by a process known as vacuum metalizing.
This metallic sealer needed to seal the cube corner reflective elements so they retain part of their retroreflectivness prior to the next step of filling the shell with a thermosetting resinous material, such as epoxy or polyurethane.
This resinous filler material encapsulate the metalized cube corner reflective elements and give the marker the structural body. Finally, a layer of relatively course sand or glass beads dispersed over the top surface of the filler material prior to solidification of the filler material. This top surface will be the marker's base. Part of the sand particles will remain partially protruding above this planar surface of the marker base, thereby increase the adhesive welding parameter of the base surface. The protruded sand will improve adhesion to substrate, regardless of the type of adhesive used. This type of markers worked well for six or seven months, however, due to poor abrasion and impact resistant of the thermoplastic shell, over 60% of the reflectivity lost thereafter. Also, incompatibility of the shell material to the resinous filler material causes pealing of the reflective face or the shell, thereby losing retroreflectivity. Several attempt were made to improve abrasion resistant of the reflective face.
One was the use of thin layer of untempered glass as disclosed in U.S. Pat. No. 4,340,319, another attempt was the use of polymeric coating of the reflective face, as disclosed in U.S. Pat. No. 4,753,548 to (Forrer). These abrasion resistant coating proving to be expensive and tend to reduce retro reflectivity. Other major development in the pavement marker art has been made, this was achieved by eliminate the use of the metalized sealer for the cube corner reflective elements. By dividing the inside surface of the reflective face into reflective cells, each cell will have several cube corner reflective elements, the cells isolated from each other by partition and load carrying walls. The reflective faces welded to corresponding recesses within a hollowed body.
This method is disclosed in U.S. Pat. No. 4,227,772 (Heenan); U.S. Pat. No. 4,232,979; and U.S. Pat. No. 4,340,319 (Johnson et al); U.S. Pat. No. 4,498,733 (Flanagan). These markers proved to be superior in reflectivity, however, lack of structural strength and poor adhesion cause short life cycle for this type of markers. This applicant successfully developed two multi-cell reflective roadway markers. One roadway marker utilizes raised rhombic shaped abrasion reducing and load transferring raised ridges, said ridges intercede abrasion elements and impact load. The shell filled with epoxy, hence, the marker body having a base with large wetting parameter for shear and flexural strength, as disclosed in U.S. Pat. No. 4,726,706. The second roadway marker of this applicant, U.S. Pat. No. 5,927,897 developed a mean to increase the abrasion resistant of the reflective face by coating the reflective face with diamond-like film and by having holding pins extending from the partition walls into the body, the holding pins sealed by the filler material; this works very effectively. The entire above reflective pavement markers are incorporated herein by reference in their entireties. The present goal of Applicant is to have a durable roadway marker with high reflectance, abrasion resistant, low cost, marker base area with good welding parameter and one-step process to manufacture said reflective pavement marker.